The primary parameter correlating the viscous behavior of all newtonian fluids is the dimensionless Reynolds number:
where V is the velocity and L is the length scales of the flow.
Generally, the first thing a fluids engineer should do is estimate the Reynolds number range of the flow under study. Very low Re indicates viscous creeping motion, where inertia effects are negligible. A moderate Re imiplies a smoothly varying laminar flow. High Re probably indicates turbulent flow, which is slowly varying in the time-mean but has superimposed strong random high-frequency fluctuations. Explicit numerical values for low, moderate, and high Reynolds numbers cannot be stated here.